1. Field of the Invention
The present invention relates to a traffic supervisory method for supervising packets to determine whether or not the packets violate a traffic characteristic in a packet switching method or an asynchronous transfer mode (ATM) switching method and a traffic supervisory apparatus for performing the method.
2. Description of Background
Generally, for example, in a packet switched network in which virtual channels are set up among terminals and a regular transmission quality is guaranteed, a call set up control is required to set up the virtual channels. The call set up control is performed for guaranteeing a regular transmission quality of a virtual channel by predicting a certain transmission quality decided by allocating the virtual channel to a terminal when a call set up request occurs and rejecting the call set up request when the predicted transmission quality is inferior to a required transmission quality.
The prediction of the transmission quality is performed according to each traffic characteristic of a virtual channel. For example, the prediction is performed by utilizing one specific value declared as the traffic characteristic by the terminal or utilizing another specific value registered in advance as the traffic characteristic.
A traffic characteristic is defined as a peak rate of generated packets, an average rate, a burst property, and the like. In particular, a method has been proposed to provide the traffic characteristic by utilizing a regular period time T and the maximum number N of packets generated within the regular period time T.
However, even if a call set up is performed by a call set up control, a requested transmission quality is not satisfied in practice when a packet violating the declared traffic characteristic is generated in a call during an actual communication. Therefore, each packet must be supervised to determine whether or not the packet generated at one virtual channel violates the traffic characteristic utilized for the set up control, to reject a violating packet when the violation occurs, and to avoid extending an adverse influence to the transmission quality of the other virtual channels.
Also, the generation of the packets in each terminal must be controlled to generate the packets according to the declared traffic characteristic.
Therefore, a conventional traffic supervisory method has been proposed as follows. In the method, the traffic characteristic is provided by utilizing a regular period time T and the maximum number N of packets generated within the regular period time T as mentioned above. Then, the number of packets generated within the regular period time T is measured and the packets generated beyond N in number are judged to violate the traffic characteristic so that the violating packets are rejected.
However, when the traffic characteristic is supervised by utilizing the above method, a drawback is, for example, produced in the generation of the packets shown in FIG. 1
FIG. 1 shows the highest degree of traffic deviation in the conventional art.
As shown in FIG. 1, in the case where a group of packets (N in number) is intensively generated at a peak rate N/T.sub.0 at the latter period T.sub.0 of a first regular period time T and another group of packets (N in number) is also intensively generated at a peak rate N/T.sub.0 at the first period T.sub.0 of a second regular period time T, a group of packets exceeding N in number is detected between a first measuring time t1 and a second measuring time t2 when a starting point t3 of the terminal cycle at which the terminal generates the packets differs from another starting point t1 of the supervising cycle in a packet switched network.
Therefore, even if a group of packets (N in number) is generated in a terminal in one cycle according to a traffic characteristic which is assigned to the terminal, in the packet switched network it is determined whether more packets have been generated than a predetermined value N. That is, the packets are judged to violate the assigned traffic characteristic.
To avoid the above judgement, the coincidence of two types of cycles must be guaranteed. One type of cycle is utilized at the terminals and another type of cycle is utilized in the switched network. However, it is not easy to control both cycles.
Also, whenever a plurality of terminals connected with a multiplexed line through a multiplexing device to efficiently utilize a subscriber's line and many packets which are respectively transmitted through corresponding virtual channels arrive at a multiplexing device to be multiplexed, statistical fluctuation is generated at the time intervals determined by the multiplexed packets.
In detail, as shown in FIG. 2, because a group of packets A is multiplexed with another group of packets B in order of the generation, time intervals T1, T2 between packets are for example changed to time intervals T1', T2'. Therefore, even if the packets A are generated at a terminal A according to the assigned traffic characteristic, the packets A are shifted in the multiplexing device so that the assigned traffic characteristic is not satisfied at the outlet of the multiplexing device.
Therefore, when the traffic supervision is performed, it is judged that the packets violate the assigned traffic characteristic even if the packets are generated in the terminal according to the assigned traffic characteristic.
Moreover, when a single virtual channel in a subscriber's loop is utilized for communication, the packets generated by an end user are provided to the multiplexing device. Therefore, the peak rate in the virtual channel can be supervised.
However, the end users sometimes communicate with each other by multiplexing a plurality of virtual channels to the single subscriber's loop by utilizing a private branch exchange (PBX) to efficiently utilize the subscriber's loop. In this case, it is impossible to avoid the statistical fluctuation at the arrival intervals of the packets generated by the multiplexing process without utilizing a specific multiplexing method by assigning a regular time slot to each virtual channel.
Therefore, even if the packets are generated in each virtual channel according to a predetermined peak rate, the arrival interval of the packets is sometimes shortened less than the minimum interval decided by the predetermined peak rate in the peak rate supervisory location of the multiplexing device. For the above reason, in the conventional peak rate supervisory method, the packets generated in the terminal according to the assigned traffic characteristic are judged to violate the assigned traffic characteristic.